1. Field of the Invention
This invention relates to magnetic recording disk drives, and more particularly to disk drives that have a fly-height actuator for controlling the spacing between the read/write head and the disk.
2. Description of the Related Art
Magnetic recording hard disk drives use a read/write transducer or head mounted on a head carrier for reading and/or writing data to the disk. The head carrier is typically an air-bearing slider attached to an actuator arm by a suspension and positioned very close to the disk surface by the suspension. There are typically a stack of disks in the disk drive with a slider-suspension assembly associated with each disk surface in the stack.
The separation or spacing between the head and the disk surface is called the fly-height. The slider has a disk-facing air-bearing surface (ABS) that causes the slider to ride on a cushion or bearing of air generated by rotation of the disk. The slider is attached to a flexure on the suspension and the suspension includes a load beam that applies a load force to the slider to counteract the air-bearing force while permitting the slider to “pitch” and “roll”. The flying dynamics of the slider and thus the fly-height are influenced by factors such as the rotation speed of the disk, the aerodynamic shape of the slider's ABS, the load force applied to the slider by the suspension, and the pitch and roll torques applied to the slider by the suspension.
Disk drives have been proposed that use a fly-height actuator for changing the spacing between the head and the disk surface. One type of fly-height actuator is a thermal actuator with an electrically-resistive heater located on the slider near the head. When current is applied to the heater the heater expands and causes the head to expand and thus move closer to the disk surface.
Disk drives with thermal fly-height actuators typically adjust the fly-height depending on the radial location, i.e., the data track, where the head is reading or writing data. This is typically accomplished by determining the optimal head-disk spacing for each of a plurality of radial bands of data tracks during manufacturing, and then storing a set of control signal values in the disk drive. During operation of the disk drive the data track where data is to be read or written is identified, and the appropriate control signal value is recalled and used to apply a corresponding level of heater power to the heater to set the head-disk spacing to the optimal value for the band in which the data track is located.
Even in the absence of heat to the heater, the write head experiences protrusion during a write operation as a result of heat from the write coil. Thus when conventional thermal fly-height control is applied during writing the first few data sectors of a continuous multiple-sector write may have a higher error rate than later-written data sectors because the write head is still at its ambient temperature and thus has no protrusion. This results in a higher-than-optimal flying height over these initial data sectors and thus weaker writability. Also, if the heater is activated during certain seeks (i.e., when the head is being moved from one data track to another data track), there may be a higher risk of head-disk contact, including head crashes that result in unrecoverable disk drive failure.
What is needed is a disk drive with a thermal fly-height actuator that has an improved method of operating the fly-height actuator.